1. Field of the Invention
The present invention relates to an exhaust gas recirculation apparatus of an engine with a supercharger to allow part of exhaust gas discharged from the supercharger-equipped engine to an exhaust passage to flow as exhaust recirculation gas in an intake passage to return to the engine.
2. Related Art
Conventionally, an exhaust gas recirculation (EGR) apparatus of an engine for a car is arranged to allow part of exhaust gas discharged after combustion from a combustion chamber of the engine to an exhaust passage to flow as EGR gas into an intake passage via an EGR passage, so that the exhaust gas is mixed with intake air flowing in the intake passage and returns to the combustion chamber. The EGR gas flowing in the EGR passage is regulated by an EGR valve provided in the EGR passage. This EGR can reduce mainly nitrogen oxide (NOx) in the exhaust gas and improve fuel consumption during a partial load operation of the engine.
Exhaust gas from the engine contains no oxygen or is in an oxygen lean state. Thus, when part of the exhaust gas is mixed with the intake air by EGR, the oxygen concentration of the intake air decreases. In a combustion chamber, therefore, fuel burns in a low oxygen concentration. Thus, a peak temperature during combustion decreases, thereby suppressing the occurrence of NOx. In a gasoline engine, even when the content of oxygen in intake air is not increased by EGR and a throttle valve is closed to some degree, it is possible to reduce pumping loss of the engine.
Herein, recently, it is conceivable to perform EGR in the entire operating region of the engine in order to further improve fuel consumption. Realization of high EGR rates is thus demanded. To realize the high EGR rates, it is necessary for conventional arts to increase the internal diameter of an EGR passage or increase the opening area of a flow passage provided by a valve element and a valve seat of an EGR valve.
Meanwhile, it is also known to provide the EGR apparatus to an engine equipped with a supercharger. Japanese patent application publication No. JP-A-2012-229679 discloses a low pressure loop EGR apparatus to be mounted in a supercharger-equipped engine of this type. This supercharger includes a turbine placed in an exhaust passage and a compressor placed in an intake passage and driven by the turbine. This EGR apparatus includes an EGR passage provided between the exhaust passage downstream of the turbine and the intake passage upstream of the compressor, and an EGR valve provided in the EGR passage. To prevent corrosion due to condensed water generated in the EGR passage while addressing a demand for strict NOx reduction, this EGR apparatus is configured to close the EGR valve as needed to thereby limit a recirculation amount of EGR gas.